Available in many shapes and sizes, insulation inserts add thermal resistance to concrete masonry walls without increasing the wall thickness or hiding the masonry's beauty. The preformed inserts are placed in block cores. Most types are installed at the block plant, but some are installed on the jobsite after the block are laid. Insulation inserts for concrete masonry usually are made of polystyrene. Several types of inserts are available. Some are made to fit the cores of standard-size concrete block. Others are made to fit block specially designed for thermal efficiency. Some inserts fit inside only one block core. Others fit inside several block cores at one time. INSERTS FOR SPECIALLY DESIGNED BLOCK Several manufacturers have designed special concrete block shapes to take more advantage of insulation inserts. Both the block and the inserts are designed together as one system. To reduce thermal bridging (heat flow through low-resistance materials that penetrate the insulation), several of these manufacturers have reduced the cross-section of the block webs. PLACE INSERTS ON THE EXTERIOR SIDE OF CORES For inserts that don't fully fill the block core, the installer must decide where to place them in the cores--in the middle or against the indoor or outdoor side of the core. Most insert manufacturers recommend placing inserts against the core side that will be toward the exterior of the building.